text: There are suggestions that depletion forces may be a significant contributor in some biological systems, specifically in membrane interactions between cells or any membranous structure. With concentrations of large molecules such as proteins or carbohydrates in the extracellular matrix, it is likely some depletion force effects are observed between cells or vesicles that are very close. However, due to the complexity of most biological systems, it is difficult to determine how much these depletion forces influence membrane interactions. Models of vesicle interactions with depletion forces have been developed, but these are greatly simplified and their applicability to real biological systems is questionable.